The present invention relates to photo choppers, and relates more particularly to a photo chopper circuit for connection to the power supply line, voltage detection line, and ground terminal of a satellite antenna allocator wherein if the photo chopper is erroneously connected to the voltage line of the satellite antenna allocator for motor drive or the power supply line of the satellite antenna allocator, its overvoltage detection/control device is turned on to switch off the power switch or, its protective diode reverses flow of voltage to protect the photo chopper.
FIG. 3 shows a photo chopper according to the prior art, which is generally comprised of an infrared emitting diode LED, a photoresistor OPT, a plurality of resistors R11, R12, and R13, and a transistor Q1. The emitter of the phototransistor OPT is respectively connected to one end of the emitter resistor R12 and the base of the transistor Q1. The collector of the phototransistor OPT is respectively connected to one end of the resistor R11 and the +5 V power supply terminal of the satellite antenna allocator 10. The opposite end of the resistor R11 is connected to the positive terminal of the infrared emitting diode LED. The negative terminal of the infrared emitting diode LED is connected to the opposite end of the resistor R12 and the emitter of the transistor Q1 and the ground (GND) terminal of the satellite antenna allocator 10. The collector of the transistor Q1 is connected to the voltage detection terminal (SENSOR) of the satellite antenna allocator 10 through the resistor R13. When the photo chopper is in use, it must be properly installed as above described. If the +5 V voltage and output voltage of the photo chopper are reversely connected to the power supply line of the satellite antenna allocator, or erroneously connected to the voltage line terminals M1 and M2 of the satellite antenna allocator for motor drive, the photo chopper will be burnt or damaged.